Improved attitude agility in small satellites increases their value by improving their data collection rate and increasing the time available for transmission of that data to the ground. This is so because a time lag exists as the satellite progresses from one attitude to another for collection or transmission of the data. The longer the progression time, the shorter the time available for data collection and transmission.
The current state-of-the art in agile small satellites allows for slew rates of less than 1°/sec. More agility in small satellites allows for new missions that were previously unachievable such as synthesized large aperture imaging, moving ground force tracking, missile tracking, tactical imaging, space superiority and space situational awareness. These new missions may need slew rates of 2°/min and faster.
In the art, reaction wheel assemblies (RWA) have been used to control attitude in smaller satellites and produce slew rates in a vehicle of 2°/min or faster. However, RWA's have an inherently low torque producing capability and may take over 60 seconds to accelerate a small satellite to this slew rate, which is unacceptably long.
Control Moment Gyroscopes (CMG) are presently the only non-expendable actuators capable of supplying high torque (i.e. equal to or greater that 1 N-m) to achieve an acceptably high slew rate. However, because of their size (approx. 16″ disk diameter), their relatively large mass and their power consumption, these devices have historically been impractical for use with small satellites (i.e. <400 kg). As a minimum, three gyros are used to control the attitude of a satellite. Therefore, CMG size is an issue. As such, there is a need for a CMG of smaller dimensions with low power consumption, while at the same time producing sufficient torque to provide sufficient attitude agility.